My '70 145S booster has broken diaphram. Before I disconnected the vacuum line it hissed slightly. Also, it won't hold vacuum when pumped up with Mightyvac tester (lots of pumps to evacuate the large volume of the booster). Agree that it is odd that it works intermittantly -- usually they fail by bursting the diaphram.

Ain't no big deal to disconnect booster vacuum and plug vacuum port - you just have to push harder on the brake pedal. I'm driving both my 260Z and 145S like that. But my sport enthusiast buddies tell me that booster in service is much prefered for improved braking control sensitivity.

I got a replacement booster for the '70 145S from RPR Volvo http://www.rprusa.com/
but it's still sitting in my garage. (One of 20,000,000 to-do projects, and not to close to the top of the list.) Don't know if it is rebuilt or new or what.

Supposedly you can change the booster without disconnecting the hydraulic lines from the master cylinder, but I have not tried that yet.

Later,
Al